I'm using a Micrel KSZ8051 Phy in a 100mbps design. The datasheet specifies that it should have a small ferrite bead feeding the power.
However, the datasheet doesn't suggest any specifications for the ferrite. What should I consider when choosing a ferrite? Do I simply select the component with the highest impedance at 100MHz which can take the current?
Best Answer
It's old school good practice. If you redesign your schematic, you will see a PI filter composed by two capacitors before, two capacitors after the inductor. It will prevent inrush high speed vdd fluctuations from the digital part of the chip, vddIO, to the analog part, vdda. At 100mbps any small ferrite will do. Pay attention on wire geometry in this region!